The present invention refers to a plate heat exchanger, which includes a sensor device and a plate package of heat transfer plates, which are provided to form, between the plates, first passages for a first fluid and second passages for a second fluid, wherein the sensor device includes a space, which is closed to the first passages and the second passages, wherein the closed space is arranged to contain a medium, which is provided to be influenced by the temperature of at least one of said fluids, and to be connectable to means for sensing a pressure change of said medium in the closed space.
EP-B-608 195 discloses such a plate heat exchanger with a sensor device, which includes a temperature sensor with an elongated shape. The temperature sensor extends in one of the porthole channels of the plate heat exchanger, which communicates with some of the heat transfer passages of the plate package. The temperature sensor communicates via a so-called capillary tube having a valve for controlling a flow of district heating water, for instance, through the plate heat exchanger.
WO97/00415 discloses a plate heat exchanger which is intended to be used as an oil cooler. The heat exchanger includes a valve, which is influenced by a sensor of another type, namely a temperature sensitive spring, which is mounted in a housing at a porthole channel of the heat exchanger. The valve opens and closes a bypass channel in the heat exchanger.
DK-U-9600205 discloses a plate heat exchanger, which is provided with a space arranged outside the plate heat exchanger and extending at an outer surface of the plate heat exchanger. An elongated temperature sensor is provided in the space. The space communicates with passages for one of the fluids in the plate heat exchanger. The space is provided in the proximity of one inlet or outlet opening of the heat exchanger. The temperature sensor is arranged to co-operate with equipment for controlling a flow of one of the fluids through the plate heat exchanger.
Each of these documents thus proposes the provision of a separate sensor outside the plate heat exchanger or in any of the porthole channels of the plate heat exchanger. The provision of such a separate sensor is difficult from a manufacturing point of view. Furthermore, a sensor in any of the porthole channels results in an increased flow resistance, not only due to the sensor proper but also due to the components required for attaching the sensor in the porthole channel. The known arrangements also have the disadvantage that the time constant is long, i.e. it takes a relatively long time before a temperature change of one or both fluids results in a sufficient influence on said medium and thus in a desired change of a valve position, for instance.